Not applicable.
Alfalfa (Medicago sativa) has often been referred to as the xe2x80x9cQueen of Foragesxe2x80x9d because it is an excellent source of protein and digestible fiber, and because its wide adaptation. Alfalfa is highly effective in nitrogen fixation, and is frequently planted in crop rotation to replenish nutrients depleted from the soil by other crops such as corn.
Efforts to develop alfalfa varieties having improved traits and increased production have focused on breeding for disease, insect, or nematode resistance, persistence, adaptation to specific environments, increased yield, and improved quality. Breeders have had less success in breeding for yield and quality per se, although methods directed toward increasing herbage quality and forage yield have been developed. For example, see U.S. Pat. No. 4,045,912, which is incorporated herein by reference.
Breeding programs typically emphasize maximizing heterogeneity of a given alfalfa variety to improve yield and stability. However, this generally results in wide variations in characteristics such as flowering dates, flowering frequency, development rate, growth rate, fall dormancy and winter hardiness. Prior art breeding methods do not emphasize improving the uniformity of these characteristics.
An important economic consideration in the development of hybrid alfalfa strains is the ability of such hybrids to produce acceptable yields of alfalfa seed. U.S. Pat. No. 4,045,912, incorporated by reference herein, discloses a process for producing alfalfa seed by random pollination of male sterile plants (produced by a cross of a cytoplasmic male sterile line and maintainer alfalfa line) and a male fertile line, with the ratio of male sterile plants to male fertile plants in the range of from 1:1 to 3:1.
There is a need in the art for producing alfalfa hybrids having agronomically desirable traits and breeding methods that result in a high degree of hybridity, uniformity of selected traits, and acceptable seed yields.
In one aspect, the present invention provides a Medicago sativa hybrid seed or cultivated alfalfa seed designated DS9705 Hyb ((A833xc3x97B209)xc3x97(Thor, DS9761 and C580)), and deposited under the terms of the Budapest Treaty on Dec. 4, 2000 with the America Type Culture Collection (ATCC), Manassas, Va., under Accession Number PTA-2759.
The present invention includes a Medicago sativa hybrid plant or cultivated alfalfa plant derived from the seed deposited under Accession Number PTA-2759. The plant may be grown directly from the seed deposited under Accession Number PTA-2759, or may be obtained indirectly from a plant grown directly from the seed by any suitable means. For example, the plant may be generated from seed produced by a plant grown directly from the seed, from a cutting taken from a plant grown directly from the seed, or from tissue culture or callous derived from cells from a plant grown directly from the seed. The invention includes succeeding generations of plants derived from plants grown from the seed of Accession Number PTA-2759.
In other aspects, the present invention includes the pollen and ovule of a plant derived from the seed deposited under Accession Number PTA-2759.
In another aspect, the present invention provides a method of producing alfalfa seeds having at least 75% hybridity comprising the steps of: crossing cytoplasmic male sterile alfalfa plants with maintainer alfalfa plants to produce cytoplasmic male sterile hybrid seed; selectively harvesting seed from the cytoplasmic male sterile plants; crossing plants grown from the seed of male sterile hybrid plants by male fertile alfalfa plants by pollination by growing the seed from male sterile hybrid plants with seed from at least one male fertile alfalfa plant, the male sterile and male fertile seed planted at a ratio of about four male sterile seeds to every one male fertile seed; and non-selectively recovering seeds from the pollinated alfalfa plants.
Another aspect of the invention provides seed comprising at least 75% hybrid seed, the seed produced by crossing cytoplasmic male sterile alfalfa plants with maintainer alfalfa plants to produce cytoplasmic male sterile hybrid seed; selectively harvesting seed from the cytoplasmic male sterile plants; crossing plants grown from the seed of male sterile hybrid plants by male fertile alfalfa plants by pollination by growing the seed from male sterile hybrid plants with seed from at least one male fertile alfalfa plant, the male sterile and male fertile seed planted at a ratio of about four male sterile seeds to every one male fertile seed; and non-selectively recovering seeds from the pollinated alfalfa plants.
Optionally, the percentage hybridity can be verified using either genetic or morphological markers.
It is an advantage of the present invention that the method of producing hybrid alfalfa seed results in seed with at least 75% hybridity in commercially acceptable yields.
It is an advantage that any cytoplasmic male sterile alfalfa plants and maintainer alfalfa plants may be selected for use in the practice of the present invention to obtain a cytoplasmic male sterile hybrid plant.
It is a further advantage of the present invention that the forage yields of fields planted with 75% hybrid alfalfa are comparable to forage yields of fields planted with 100% hybrid seed, a feature that allows for high forage yields and high seed production.
Other features and advantages of the invention will be apparent upon review of the specification.